Electronic discharge device



May 16, 1950 R. c. GEE ET AL 2,507,706

ELECTRONIC DISCHARGE DEVICE Filed Jan. 17, 1948 3 Sheets-Sheet l R. c. 655 m GRONROS AT TORNEV May 16, 1950 R. c. GEE ETAL ELECTRONIC DISCHARGE DEVICE 3 Sheets-Sheet 2 Filed Jani 17, 1948 R. c. 655 [NM/;MS m GRONROS ATTORNEV May 16, 1950 R. c. GEE ET AL 9 3 ELECTRONIC DISCHARGE DEVICE Filed Jan. 17, 1948 5 Sheets-Sheet 3 RC. GEE /Nl/ENTORS- W GRONROS AT TORNEV atentecl May 6, 1950 ELECTRONIC DISCHARGE DEVICE Richard C. Gee, Saddle River Township, Bergen County, N'. J., and Warren Gro'nros, New York, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a. Corporation of New York Application January 17, 1948, Serial No. 2,825

Claims. 1

This' invention relates` to electronic discharge devices and more particularly to such devices of the' micro-midget multi-element type especially useful' in* Very high' and ultra-high freque'ncy translating systems.

The static charaeteristics of electronic discharge deyicesdetermne the scope of use and the efiicienc'y of operation inlow frequenoy applications. l'oweyer, the requirements encountered in the:` very high and ultra-high frequenoy ranges, for' example in= the 109 to &OO-megacycle range, impose conditions which* can' only be satisfied by extremely precise correlation of the elements to provide the essential elctricel constants whereby the-*higi estefiiciency is attaine'd. The most imp'ort'ant characteristic for general use is the transconductance; The transconductance depends on the spa'cing between the cathode, control grid and screen grid, the diameter of the grid wre, the spacing'- thereof; the" electrode area and the potentials applied to`the-electrodes In order to attain a high'transconductance, it is necessary to reduce the diameter'of' the control grid wire to a point where the 'wire 'is' not' self -supporting when wound in g rid form; Therefore, the fine fragile wire is wotnd on a' support france which maintains the collateral r'elation of'` the. grid and cathode constant' at' very closespacing, for example of' the order of=2 mils. In addition, the grid laterals must 'be 'relatively close together along the length of the grid to'secure the desired controlling action upon* the electron stream emanating fromthe catho'de;

This arrangement'- presente" certain difiiculties dhe:: to the stren`gthen`in cenguration of the frame which introduce's' solid metallic` portions between the cath'ode and anocle at opposite ends of the `grid structure'. These portions increase the* grid-plate Capacity so that the' performance ofthe deviceisdegraded in some applications.

An object of this invention' isto reduce the plate-gridcapacitance in discharge devices employing r'ame grid structures.

Ahother'objct of theinvention 'is to secure extremely high transconductance in high frequency These objects are realized in` accordance' with features ofthis invention in' an electronic 'discharge devce of the micro-midget type having a frame' type grid assembly,' by includingshielding :sections on the screen or positively biased-grid adjacen't the control grid 'to reduce the parasitic 2 Capacity of the (control grid in relation to the" anodel A specific manner in which this is aceomplishedis'to terminate the usual lateral windin 'of the screen grid by closely wound turns *of wire at opposite nds to effectively shield'the stray Capacity fields cau'sed by the solid strap material of the frame grd structure. Since theclosely space'd' shieldngsections of the screen grid extend over the width of the bracing portions of the control grid` their eect is cancelled due to the fact that the closely spaced turns at -opposite ends form a barrier to theestablishment of a capacitance between the solid surfaces of the'anode and th b racingstraps of the control grid.

A'feature of the invention relates to the assembly of the 'screen gridincorrelation with the framo control grid-whereby the shielding sections of'the-'screen grid extend completely between the inner lat'eral edgesxo-the bracing straps and the mica spacers supporting all the electrodes in order to reduce the capacitance" between the bracing straps and-the anode.

lAnother feature of' the `invention pertains to the maintenance of critical collateral space relation between the large area cathode surface'and the'closely spaced control grid laterals. As these elements are onl spaced apart by a distance of the order of 2%; -mils it isi essential that the cathode bejheldin lts proper position. This is accomplished -by accurately forming the' slots' in the spacing nica' discs on opposite ends of? he unita'ry' assembly to a ccommodate the semicircular form of the frame grid structure and providing limited" contact fingers on the micas in the opening forthe flat cathode so that the cathode cannot' move lateraily in its relation'to the control `-grid These.ngersabut'against the fiat prtions of-thecathode"surfaces on opposte sides and at the top andb'ottom'thereof so that the cathode' is'accurate'ly" spaced in constant relation toi the laterafl' Wires of the'control gricl structure. These and'other'features and advantages of the invehtion will' be more-'clearly set' orth in' the following detai'led description of an' illustrative einbodiinent sh'b'w'n 4 in the accompanying drawi''gs in' which:

Eigi 1 is an' elevational View partly in section, on algreatly nlarged scale, of an electronic discharge devic'e enbodying this inVen'tOn, a portion of the 'vessel being'broken away;

Fig.- 2'is asideview in" elevation of the device of'Eig; 1 with 'the vesel broken away and the elctrofde ;nga fs'r ovyn nr 'full' lines to illustrate the asseinblyof the device; i

Figf Sfis a planview of the spacing insulator en ployed in the'deyice of Fig 1, showing the acci'ratel'ycut* apertures' for th support of theelectrodeelerrentsin the 'unit and the configuration of theicathodefopening 'in combination with' the Fig. 4 illustrates, on a greatly magnifled scale, a section of the lower portion of the electrode unit, taken on the line 4-4 of Fig. 1, the relatively close tolerances which must be maintained between the electrodes in the micro-midget device and the shielding eflect of the screen grid in relaton to the frame type control grid, this figure being shown in partly diagrammatic form in the interest of clarity.

Referring to the drawings, the electronic discharge device of micro-midget dimensions embodying this invention is shown in Fig. 1 on an enlarged scale of about 10 to 1 to clearly illustrate the components of the unitary electrode assembly mounted within the receptacle. Although the electrode unit, exclusive of mounting projections,

occupies less than half of the space in the receptacle, and the unit includes spacer discs to fit the inner wall of the receptacle, sone realization of the actual size of the electrode unit may be gained by reducing the dimensions shown by a factor of 10. Then the unit has dimensional limits of approximately one-half inch length, onehalf inch width and one-quarter inch thickness. Since the unit includes a multiplicity of coaxial electrodes of which the central cathode and surrounding control electrode must be proportionally smaller in two dimensions, namely, width and thickness, it is evident that extremely precise tolerances must be maintained in the fabrication of these elements to realize the close spacial relation in the unitary assembly. For example, the cathode has a major axis of .150 inch, a minor axis of .0245 inch and a length of .330 inch. The anode has a major axis of .470 inch, a minor axis of .190 inch and a length of .253 inch with the cooperating grid electrodes therebetween having correspondingly smaller dimensions. When these micro-dimensional elements are combined in coaxial symmetry in which the control grid is laterv ally spaced from the cathode surface a relatively close distance of the order of .0025 inch and the other electrodes are similarly spaced at varying distances from each other, it is evident that precision is required in the mounting and relationship of these elements to attain the electrical constants required in the operation of the device.

The device, as shown in Fig. 1, includes a highly evacuated vitreous enclosing vessel ID, of cylindrical configuration, having a molded or cast stem ll sealed to the base end, the stern having integral internal embossments [2 forming pillar reinforcements for a plurality of hermetically sealed lead-in wires or conductors l3 which terminate exterior to the stern as rigid terminal pins !4 adapted to engage socket contacts for coupling the device in various applications. The opposite end of the vessel is closed by a sealing tubulation !5 for processing the device in the final assembly in which the tubulation is sealed. to a vacuum pump station to remove air and occluded gases and create a high vacuum within the vessel after which the tubulation is sealed off.

The electrode unit or mount within the vessel is resiliently supported from the cylindrical wall of the vessel through mioa spacer discs IG and IT which are provided with spaced projections l8 around the periphery, as shown in Fig. 3, to engage the inner wall and late'ally support the unit in fixed position in the vessel. The unit is anchored therein by rigid connection of the electrodes to the lead-in wires in the stem. The mica discs !6 and I'I are precision cut, as shown in Fig. 3, with various shapes of slots and apertures to provide accurately allgned support openings which aid, in part, in determinng the relationship and spacial cooperation of the respective electrodes involved in the particular mount assembly.

The cathode !9 forms the central main electrode of the unit and is rectangular in crosssection to provide a large surface for the emission of electrons toward the other electrodes in the unit. An internal insulated heater element 20, of hairpin formation, is enclosed by the cathode to indirectly heat the cathode and raise the cathode to the proper temperature for electron emission. A frame type control electrode ZI, which is disclosed in more detail and claimed in a copending application, Serial No. 2,433, filed January 15, 1948, of E. J. Walsh, surrounds the cathode and is mounted in relatively close spacial relation to the cathode surface to attain the desired high transconductance. A screen grld 22 encircles the control electrode and another wire wound grid or suppressor electrode 23 is spaced about the screen grid. A sheet metal rectangular-shaped anode 24 having cut-out side portions is mounted in surrounding relation to the other internal electrodes to complete the electrode assembly of the device.

Since the cathode !9 and control grid 2! are mounted in relatively close spacial relation and must be maintained in this relation in substantial constancy to secure high efliciency and high transconductance in the device, it is evident that accuracy and mounting facilities must be provided.

In accordance with one feature of this invention, the cathode and control electrode relation is maintained in constant symmetry so that mechanical vibrations of the cathode do not alter the collateral spacing of these electrodes. This is accomplished by the configuration of the mounting slots in the mica spacer discs, as shown in Fig. 3. The elongated slot 25 is formed in the center of the disc and extends along one diameter equal to the major transverse dimension of the cathode !9, the latter being provided with bead projections 26 which fit against the inside surface of each disc to support the cathode between the top and bottom spacer discs of the unit assembly. The long sides of the slot 25 are provided with corner angles 21 equivalent to the minor transverse dimension of the hollow cathode so that the cathode is securely locked in position within the slot. In addition, the same sides of the slot are formed with oppositely disposed and inwardly 'projecting broad flat surface integral fingers or contact lugs 28 which engage the major surfaces of the cathode and insure rigid mounting thereof. However, the wider spaces or openings in the slot 25 between the fingers reduce the area of contact between the cathode sleeve and the slot eectively to reduce the conduction of' heat from the cathode to the mica spacer discs. This reduction in conduction loss is essential to provide uniform heating of the active cathode surfaces and to effect economy in power input to the cathode. Heat conduction loss into the spacer discs would be excessive were the slots 25 made to engage snugly the entire periphery of the cathode sleeve; yet, if the slots were made large enough to provide loose fit of the cathode within them, thus achieving mere random point contact between cathode and discs to realize the desired reduction in heat conduction path, then the cathode could not be positioned accurately with respect to the control grid and would be sub- 57 ject to relatively sizeable migrations because 'of external mechanical impulses. This rigidity of mounting of the cathode in a lateral direction is .to prevent variation in relaton of the cathode with respect to the closely spaced laterai wires `of the control grid adjaeent thereto, the spacing between them being only .0025 inch.

When the cathode is Secured in position between the mica spacer discs, the control grid 2l iswmounted around it This grid is formed ofa metallic frame having semicircularupright portions 29.Which are joined together by bracing straps 3'9a'cljacent opposite ends. The upright portions 2. are fitted into apertures 3! of simi- `larshaped Outline in the mica discs and the straps 38 abut against the inner surfaces of the .discs to, rigidly support the grid in relation to the cathode surface. The frame structure of the :control electrode insures constant laterality of thefine grid helix Wire 32 closely adjacent the `large; area of the flat cathode surface. The brac- .ing strapslnot only increase the rigidity of the frame assembly and form a broad base in contactlwith the mica spacer discs but also provide ta sharp. cut-off in` the emission characteristic of the cathcde. This is the case because the emission coating 33. on the cathode surface, as shown in Fig. 4, is not` uniform at the extremities, as indicated at 34, and the Wide straps 3@ of the .control .grid correct for" this defect by blocking .the extremities of the cathode coating thereby preventing passage of emission from the end portions ofthe cathode.

The bracing straps Sii of the control grid 21,

however, introduce stray capacit'ance effects between the Vcathode and the anode since they i present relatively large metallic masses in the ;spacebetween these eiectrodes, and thereby increase the capacity coupling between the input and output rcircuits of the device. This eect is overcome, inaccordance with another feature of ;this invention, by fcrming shielding portions on ,the ends of the screen grid which immediately surround the ends of the control electrode. This is-accomplished-by terminating the' winding 22 along the support Wires 35 of` the screen gridwith 24:50 that the 'Capacity eiect of the straps is cancellcd or materially diminished to a value which maybe tolerated.

p -The screen grid 22 may be spaced from the Econtrolgridlateral wires 32 a distance of 18 mils andis mounted with the support rods 35 in ;apertures' 31 and 38 in the inica discs. .It will be noted that the elongated aperture 33 permits expansion of the grid structure with temperature'changes.

The suppressor grid 23 has the lateral turns relatively widely spaced in relation to the intermediate portion of the screen grid and the very close spacing of the lateral turns of the control grid. This grid 23 is mounted on a pair of support wires 39 which extend into apertures 46 on one' side of the cathode and 38 on the other side,

'the latter aperturepermitting expansion of the -;grid 23'1atera-lly in the plane of the major lateral dimensions oi the electrodes.

The suppressor grid may be spaced approximately 16 mils from the screen grid 22.

The ,anode 24; is m med' of two. plat sections which .lie parallel to the major dimensions of the other electrodes and may be spaced approximately 44 mils from the suppressor grid surface. The anode sections are provided with pairjs of strap portions' 4'l which extend from the side edgs and theseare bent at right ,angles .with adjacenta-ngular' straps join'ed together, preferably by, welding, to form a box-shaped Construction. The opposite ends o'f'the plate sections of the anode are provided also .With projecting ears 42 which fitinto apertures 43 in the mica di scs and are bent over the outer surfaces of the discs to lock these discspto the anode.

The unit assembly is completed by mounting a transverse'toptmetallic shield 44, of U-shaped cross-section, byiclips 45 which fasten the shield to the mica disc IS through the apertures 4 6. A similar shield 41 extends across the outer surface of the bottom mica disc IT and is attachd thereto in a, similar manner. The top shield .is connected to the ,supprssor grid by. a stub wire 48 while the lower shield 41 is connected to a terminal pin; in the stem by the bent conductor 49. In addition; a'disc shield 50 is supported in spaced parallel relaton to the disc stern within the confines of the glass pillars !2 and is connected tothe conductoriis by awire 5l.

The anode ,is connected to aterminal pin by stub wireZ. 'The long. support wire. 35 of the screen grid is attached to another terminalpin by a strap 53 and the control grid long frame st'ut is connected toconductor. 54in the .stern. The theater element, 20 has' thetwo projecting ends 55 and 5 3 'connected rspectively to lower shield!" bystubwire 51 andconductor 58;in the stern. Thecathode is joined` to a conductor 59 by a resiient nickel alloy strip 68 andthe suppressor grid is tied to the same conductor as the cathode byautransverse strip 61.

Agetterstripfi is mounted on a U-sh'aped frame 63 to form a closed loop Whichmay be heatedby high frequency induction methods to vaporize-the gette'r material from the strip and the loop is supported' bya bent wire: 64 from the top shield *44.

The 'above-describedcontruction of the microdi'rnensional unit assemblyin the device provides a unit'aryrugged mounting a'ssembly of the multiple electrodes in which the space relation of the cathode and control electrode is maintained constant so that the transconductance characteristic is stabilized to insure positive and constant operation in the band of frequenci es for which the specific cooperating electrode assembly is desired to' be employed. The mounting assembly of the cathode, in combination with the frame grid construction'maintains constant parallelim between these electrodes regardless of mechanical Vibrations. Furthermore, the capacitance eects of the bracing straps of the controlgrid frame are neutralized by the shielding portions of the surrounding gridassembly so, that thespurious elds in the vicinity of the .straps of the grid' frame are prevented from reaching the anode.

While the invention hasrbeen disclosed in a particular embodiment, it is, of' course, understood that various modifications may .be made appended claims.

What is claimed is: 1. An electronic discharge device comprising an enclosing vessel, a unitary mount within said vessel including a tubular cathode, an anode surrounding said cathode, a grid adjacent the cathode having a frame type structure with bracing straps at opposite ends between the cathode and anode surfaces, and another grid located in a direction toward said anode having a winding of widely spaced turns over a portion within the compass of said frane grid winding and shielding portions intermediate said bracing straps and said anode.

2. An electronic discharge device comprising an enclosing vessel, a mount within said vessel including a tubular cathode, an anode surroundin the same, and a plurality of grid electrodes therebetween, one of said grids being a control grid adjacent the cathode and having a frame type structure with bracing straps at opposite ends parallel to said cathode and anode surfaces, and another of said grids surrounding said control grid and having means at opposite ends thereof for neutralizing the capacitance effects of said bracing straps on said frame structure.

3. An electronic discharge device comprising an enclosing vessel, a unitary mount within said vessel including a tubular cathode, an anode surrounding the same, and a plurality of grid electrodes between said cathode and anode, one of said grid electrodes adjacent the cathode having a frame type structure with bracing straps at opposite ends parallel to said cathode and anode surfaces, the next adjacent grid located in a direction toward the anode having a winding of widely spaced turns over a portion within the compass of said frame grid winding and closely spaced turns of winding at opposite ends equivalent to the expanse of said straps on said frame structure.

4. An electronic discharge device comprising an enclosing vessel, a unitary mount within said vessel including a tubular cathode, an anode surrounding the same, and a plurality of grid electrodes between said cathode and anode, the grid adjacent the cathode being a control grid having a frame type structure with bracing straps at opposite ends between said cathode and anode surfaces, and another of said grids surrounding said control grid and having shielding portions at opposite ends in longitudinal extent equivalent to said bracing straps.

5. An electronic discharge device comprising an enclosing vessel, a unitary mount within said vessel, said mount including a plurality of closely spaced cooperating electrodes and spacing insulators at opposite ends, one of said electrodes being a control grid relatively close to the cathode surface and` fcrmed of a closely wound helicai wire insuicient in itself to be self-supporting to maintain the laterals in parallel relation, a metallic frame structure supporting said wire laterals and having bracing straps at each end, another helically wound wire grid surrounding said control grid, said latter grid having uniformly spaced laterals of wider pitch over the length corresponding to the closely pitched turns of said control grid, and closely spaced turns at each end of said latter grid collateral to and coextensive with said bracing straps of said frarne structure.

6. A cathode mounting comprising a rectangular cathode, a plurality of electrodes surrounding said cathode, insulating spacer members at opposite ends of said electrodes and cathode, said members having openings through which said cathode extends, and broad fiat contact friction fingers projecting inwardly from said members. engaging said cathode and holding it centrally within said electrodes.

'7. An electronic discharge device comprising an enclosing vessel, a unitary electrode mount supported therein including a rectangular tubular' cathode and at least one closely spaced electrode surrounding said cathode, spacing insulators at opposite ends of said mount having apertures therein for the support and spacing of said cathode and electrode in precise collateral relation, and equally spaced broad flat contact friction portions on said insulators engaging the long dimension surface of said cathode to insure constant spacial relation with respect to said closely adjacent electrode.

8. An electronic discharge device comprising an enclosing vessel, a unitary electrode mount supported therein including a rectangular tubular cathode and at least one closely spaced electrode surrounding said cathode, spacing insulators at opposite ends of said mount having apertures therein for the support and spacing of said cathode and electrode in precise collateral relation, and spaced friction portions having parallel edges in contact with opposite long sides of the cathode in said insulators, the distance between opposed portions being equivalent to the outer minor dimension of said cathode.

9. An electronic discharge device comprising an enclosing vess l, a unitary electrode mount supported therein including a rectangular tubular cathode and at least one closely spaced electrode surrounding said cathode, spacin insulators at opposite ends of said mount having precision Slots and apertures therein for the mounting of said cathode and electrode, the central slot for said cathode being greater in dimension than the minor axis thereof, and a plurality of integral blunt edge tab projections extending from said central slot on each side in opposed planar relation and matching the minor axis of said cathode and rigidly mounting the cathode free from latera movement.

10. An electrom'c discharge device comprising an enclosing vessel, a unitary electrode mount supported therein including a tubular central cathode and a frame type control electrode surrounding said cathode, the uprights of said frame having a hollow semicircular configuration and said frame supporting a closely spaced lateral winding of fine wire, mica spacers at opposite ends of said mount having pairs of semicircular slots to accommodate said uprights and a central elongated slot for said cathode, the distance between the lateral winding and the surface of said cathode in collateral relation being approximately 2 /2 mils, and pairs of blunt integral extensions in said cathode slot engaging opposite sides of said cathode to maintain said relation constant.

RICHARD C. GEE. WARREN GRONROS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,138,918 Haller Dec. 6, 1938 2,206,511 McLaughlin July 2, 1940 2,286,996 Dickinson June 16, 1942 

